How much regular exercise people do now also appears to be a factor in their length.

To track the women’s movements in the study, they wore an accelerometer on their right hip for seven days in a row, during the day and night.

They were also asked to complete questionnaires on their activity.

Exercise benefits

Dr Aladdin Shadyab, lead study author, from the University of California, San Diego School of Medicine, said: “We found that women who sat for longer did not have shorter telomere length if they exercised for at least 30 minutes a day.

“Discussions about the benefits of exercise should start when we are young, and physical activity should continue to be part of our daily lives as we get older, even at 80 years old.”

The study is published in the American Journal of Epidemiology.

NHS Choices advises older adults to break up long periods of sitting with light activity because “telomerebehaviour is now considered an independent risk factor for ill health”.

It says adults aged 65 or older who are generally fit and mobile should try to do:

At least 150 minutes of moderate aerobic activity, such as cycling or walking, every week

Strength exercises on two or more days a week that work all the major muscles (legs, hips, back, abdomen, chest, shoulders and arms)

Older adults at risk of falls, or with poor balance, should also do exercises to improve balance and co-ordination at least twice a week.